Fuel such as propane may be delivered to an engine in various phases (e.g., liquid and gaseous). In some examples, only liquid propane may be delivered to the engine; however, liquid propane injection may not be favorable under relatively hot conditions. In other examples, only gaseous propane may be delivered to the engine; however, gaseous propane injection may not be favorable under relatively cool conditions. In some examples, an engine system may include a multi-phase fuel system with separate tanks for liquid and gaseous fuel injection systems, which may be costly and require a large volume of space.
One approach to address the need for separate tanks in a multi-phase fuel system is described in U.S. Pat. No. 5,479,906. In this example, a multiple phase fuel supply system is described. Liquid fuel may be injected to the engine via a plurality of port injectors and gaseous fuel may be injected to the engine via a single port injector after passing through a pressure regulator. However, U.S. Pat. No. 5,479,906 does not describe injecting gaseous fuel directly from the fuel tank to the engine without first passing through a pressure regulator, which is commonly integrated with a vaporizer.
Thus, the inventor herein has devised an approach to at least partially address the issue described above. In one example, a method for operating an engine, comprising includes, under a first condition, injecting liquid fuel to the engine. The method further includes, under a second condition, injecting vaporized liquid fuel to the engine. The method further includes, under a third condition, injecting gaseous fuel to the engine. For example, the liquid fuel may be directed from a bottom of a fuel tank to the engine, the gaseous fuel may be directed from a top of the fuel tank to the engine, and the vaporized liquid fuel may be liquid fuel from the bottom of the fuel tank directed through a vaporizer to form gaseous fuel.
Thus, an engine system may include a multi-phase fuel system which includes a single fuel tank, for example. The fuel may be injected a single phase at a time or multiple phases of fuel may be used simultaneously depending on operating conditions. For example, liquid injection may be used to increase power. Vaporized liquid fuel injection may be used for increased fuel economy and/or during relatively hot ambient conditions. Gaseous fuel injection may be used during relatively hot ambient conditions and/or when a fuel rate is low. In this way, a multi-phase fuel system may be employed while reducing cost and meeting space constraints.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.